1. Field of the Invention
The present invention relates to a venting closure assembly for a containing structure, such as a milk tank.
2. Backoround Art
In the dairy industry, milk is commonly transported from dairy farms to a central processing center by means of tank trucks and trailers. The milk-containing tank itself is generally made of stainless steel and is commonly of a double-walled construction with insulation between the inner and outer stainless steel walls, so that the contained milk can be kept at an adequately low temperature while being transported.
Because of the sanitation requirements of the dairy industry, the interior of the milk tank must be thoroughly washed at regular intervals. Also, it is necessary to provide the tank with an access opening, commonly called a "manhole", to permit an inspector to actually enter the interior of the tank. Obviously, while milk is being transported, this access opening must be properly covered both to prevent milk from being spilled out of the opening, and also to prevent outside contaiminants from being mixed with the milk. There is a further requirement that the interior of the tank be vented to the outside atmosphere, since with an airtight tank even small temperature variations in the milk would cause undersired pressure differentials between the area inside the tank and the surrounding atmosphere.
A quite common means of providing the venting in a milk tank is to provide a venting member in an interior metal cover which normally closes the access opening of the tank. This venting member generally comprises a cylindrical tube mounted to the center of the cover and extending downwardly toward the interior of the tank. The interior of the tube is provided with a set of vertically spaced, staggered baffles which overlap sufficiently to define a circuitous passageway from the interior to the exterior of the tank. An annular gasket member made of a flexible material is usually placed between the perimeter portion of the cover and the support ring which defines the tank access opening, to provide a perimeter seal. Also, an exterior dust cover is positioned over the interior cover. The sanitation standards of the dairy industry require that all components which possibly come into contact with the milk be thoroughly cleaned at regular intervals.
While the prior art disclosure assembly described above has been able to perform the closing and venting functions for a milk tank in a manner to meet the standards of the dairy industry, there was a continuing need for improvement. Accordingly, there was conceived another venting closure arrangement for a milk tank, and various embodiments of this are disclosed in U.S. Pat, 4,081,107, issued March 28, 1978, and U.S. Pat. No. 4,127,216,issued Nov. 28, 1978. In general, there is described in those patents a closure assembly where there is a venting closure member having perimeter flange members which fit against a support ring of the milk tank to form a circumferential seal and one or more circumferential venting channels. There is an outer cover having a vent opening which fits over the closure member and engages the peripheral portion thereof to form the circumferential seal against the support ring. The venting channel or channels connect to circumferentially spaced openings in the flanges to provide venting from inside the tank to the area outside the tank, while preventing both spilling of the milk and contamination from outside sources.
While the assembly described in the immediately preceeding paragraph is believed to be a substantial improvement over the earlier closure assembly described above, and while this improved assembly in general has been found to function quite well in accomplishing its intended functions, it has been found that under certain circumstances, it is possible for liquid in the containing chamber to pass out through the circumferential venting channel.
Accordingly, it is an object of the present invention to provide an improved venting closure assembly for a milk tank which performs the closure function yet more reliably, while still permitting venting of the containing structure. It is yet another object to provide such a venting closure member which is able to meet the standards of sanitation and other requirements of the dairy industry.